There is a renewed interest in high specific activity radionuclides in concentrated form, free of cold metal contaminants. One example is the Ge-68/Ga-68 generator systems for diagnostic nuclear medicine due to the spread of PET (Positron Emission Tomography) scanners for 18F FDG studies, which require a cyclotron-independent source of short-lived, positron-emitting isotope for the expanding area of receptor-specific imaging and therapy. The benefits offered by the Ge-68/Ga-68 generator system, such as the long half-life of Ge-68 (270.8 days), short half-life of Ga-68 (68 min) along with Ga-68's high positron yield, and lack of high energy gamma rays, make the system very convenient for PET. Furthermore, Ga-68 chemistry is dominated by the +3 oxidation state and is readily chelated by ligands, such as NOTA (1, 4, 7-triaazacyclononane-1,4,7-triacetic acid) and DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), which are also used to chelate radiolanthanides for use as radiopharmaceuticals.
The current commercial generators utilize Ge-68 (germanate) adsorbed onto either tin dioxide or titanium dioxide; Ga-68 is then eluted with 0.1 to 1N HCl. Unfortunately, the generators require high volumes of acid to elute the Ga-68, generally in the 5 to 20 ml range, and the eluates contain trace levels of metals such as iron, zinc, and/or titanium. The metal impurities, though present in very low levels, are also chelated by ligands, such as DOTA, and thus compete with Ga-68 for the limited number of binding sites on the target cells resulting in decreased contrast and quality of the images. Additionally it can result in higher uptake to normal tissues and, for peptides that are potent agonists, result in toxic side effects. Furthermore, it can lead to increased cost due to the excess of biomolecule that is needed which is often the most costly component of the drug.
Therefore, there is a need to provide a new and improved method and system to extract, purify, and collect a daughter isotope, from a parent/daughter source, in a relatively concentrated form and with minimum metal or other impurities. There is also a need to provide a new and improved method/system to purify and collect a high specific activity radioisotope in general.